1. Field of the Invention
The invention relates to techniques and tools to control drainage of bodily fluid from a patient and more particularly to external volume-limiting devices for withdrawing cerebrospinal fluid.
2. Description of the Related Art
There are a number of treatments for medical conditions which require fluid to be removed from an organ or tissue of a patient. One such condition is hydrocephalus, where cerebrospinal fluid abnormally accumulates in the skull faster than it is withdrawn by the body. The excessive build-up of cerebrospinal fluid compresses brain tissues, which eventually leads to brain damage.
Hydrocephalus is commonly treated by implanting a shunt in fluid communication with a ventricle within the brain to withdraw cerebrospinal fluid at a desired rate. Typically, the rate of withdrawal of cerebrospinal fluid, also referred to herein as “CSF”, is controlled by a valve having different pressure settings which a clinician adjusts pre-operatively. A number of shunt valves can be noninvasively changed after implantation, such as the Codman® Hakim® programmable valve which is currently commercially available from Codman & Shurtleff, Inc. of Raynham, Mass. Also available from Codman & Shurtleff, Inc. is the CERTAS™ programmable valve that is disclosed and claimed in U.S. Pat. No. 8,322,365 by Wilson et al.
External CSF drainage systems are typically utilized in a clinical setting when it is desirable to drain CSF through a catheter into an external “closed” collection system to prevent infection of the CSF during management of intra-cranial pressure. Removal of too much CSF, or “over-drainage”, through the catheter is undesirable and may result in severe headaches or collapse of one or more ventricular cavities within the brain. To reduce the risk of over-drainage, physicians typically drain CSF at a rate of 10 ml to 50 ml per hour.
Withdrawal of excessive CSF can also result in “over-filling” of the external drainage system. Various problems may result from over-filling, including leakage of fluid from the system and resulting infection through the pathway provided by the leaking fluid.
Many conventional drainage systems crudely control flow rate of CSF by adjusting the level at the which the system is positioned above the head or spine of the patient. In other words, gravity and fluid pressure generated within the patient and within the system affect flow rate into a collection chamber. Flow may unexpectedly increase if the level of the system is lowered in relation to the level of the catheter entering the patient, such as when a patient sits up after lying in a prone position.
One system disclosed by Eckermann in U.S. Patent Publication No. 2009/0054857 attempts to measure the volume of fluid in a collection chamber utilizing one or more sensors. In other words, proper functioning of this system appears to require correct operation of the sensors.
Another system disclosed by Hoffman et al. in U.S. Pat. No. 8,221,366 utilizes a buoyant float to seal an inflow port or a vent port of a chamber. However, this system is not optimal because the volume of the chamber appears to be fixed. Thus, the float does not appear to be adjustable to accommodate different volumes of CSF fluid if a physician selects an alternate volume of CSF to be drained.
It is therefore desirable to have a simple yet reliable and adjustable system and technique to drain bodily fluids such as cerebrospinal fluid.